Phosphate buffering in mangrove sediment pore water under eutrophication and deforestation influences.

Phosphorus (P) behavior was evaluated in mangrove wetlands impacted by urban sewage, including a deforested site. Sediment cores were analyzed for grain size, organic carbon, total nitrogen, stable isotopes (δ13C and δ15N), P contents, and pore water PO43- concentrations and net consumption/production rates. Under stronger eutrophication influence, significantly higher P (1390 vs. <1000 µg/g), δ15N (8.9 vs. <6.7 ‰) and algal material contents (with lower C/N ratio and heavier δ13C) occurred. Depth-integrated PO43- consumption rates in eutrophicated sites were up to two orders of magnitude higher (at the deforested site) than in a moderately preserved mangrove. The whole core of the moderately preserved site presented no saturation of PO43- buffering capacity, while more eutrophicated sites developed buffering zones saturated at ∼18-26 cm depth. Contrasting to nearby subtidal environments, eutrophication did not cause larger pore water PO43- concentration, evidencing the role of PO43- buffering on P filtering by mangrove wetlands.

Linking centennial scale anthropogenic changes and sedimentary records as lessons for urban coastal management.

Coastal eutrophication and urban flooding are increasingly important components of global change. Although increased seawater renewal by barrier openings and channelizing are common mitigation measures in coastal lagoons worldwide, their effects on these ecosystems are not fully understood. Here, we evaluated the relationships between human interventions in the watershed, artificial connections to the sea, and the sediment burial rates in an urban coastal lagoon (Maricá lagoon, Southeastern Brazil). Sediment accretion along with nutrient and carbon burial rates were determined in two sediment cores representing the past ∼120 years (210Pb dating) and associated with anthropogenic changes as indicated by historical records and geoinformation analyses. Lagoon infilling and eutrophication, expressed by the average sediment accretion, TP, TN, and OC burial rates, respectively, increased ∼9-18, 13-15, 11-14 and 11-12-fold from the earliest (<1950) to the most recent (2000-2017) period. These multi-proxy records confirm mechanistic links between deforestation, urbanization, and untreated sewage discharges. In addition, our findings reveal artificial connections to the sea may contribute to lagoonal eutrophication and infilling, particularly when not integrated with sewage treatment and forest conservation or reforestation in the watershed. Therefore, increased seawater renewal by physical interventions commonly considered as mitigation measures may in contrast cause severe degradation in coastal lagoons, causing harmful consequences that should be not neglected when implementing management practices.

Carbonate system in the Cabo Frio upwelling.

The quantitative assessment of the carbonate system represents one of the biggest challenges toward the "Sustainable Development Goals" defined by the United Nations in 2015. In this sense, the present study investigated the Spatio-temporal dynamics of the carbonate system and the effects of the El Niño and La Niña phenomena over the Cabo Frio upwelling area. The physical characterization of the site was carried out through data on wind speed and sea surface temperature. Water samples were also collected during the oceanographic cruise onboard the Diadorim R/V (Research Vessel). From these samples, the parameters of absolute and practical salinity, density, pH, total alkalinity, carbonate, calcite, aragonite, bicarbonate dissolved inorganic carbon, carbon dioxide, partial pressure of carbon, calcium, and total boron were obtained. The highest average concentration of bicarbonate in S1 (2018 µmol/kg) seems to contribute to the dissolved inorganic carbon values (2203 µmol/kg). The values of calcite saturation state, aragonite saturation state, and carbonate were higher on the surface of each station (calcite saturation state = 4.80-5.48; aragonite saturation state = 3.10-3.63, and carbonate = 189-216 µmol/kg). The mean values of pH were similar in the day/night samples (7.96/7.97). The whole carbonate system was calculated through thermodynamic modeling with the Marine Chemical Analysis (AQM) program loaded with the results of the following parameters: temperature, salinity, total alkalinity, and pH parameters. This manuscript presents original data on the carbonate system and the "acidification" process influenced by the Cabo Frio upwelling, which directly depends on the El Niño and La Niña phenomena oscillations in the sea surface temperature.

Linking eutrophication to carbon dioxide and methane emissions from exposed mangrove soils along an urban gradient.

Mangroves are one of the most important but threatened blue carbon ecosystems globally. Rapid urban growth has resulted in nutrient inputs and subsequent coastal eutrophication, associated with an enrichment in organic matter (OM) from algal and sewage sources and substantial changes in greenhouse gas (GHG) emissions. However, the effects of nitrogen (N) and phosphorus (P) enrichment on mangrove soil OM composition and GHG emissions, such as methane (CH4) and carbon dioxide (CO2), are still poorly understood. Here, we aim to evaluate the relationships between CO2 and CH4 efflux with OM composition in exposed soils from three mangrove areas along watersheds with different urbanization levels (Rio de Janeiro State, Brazil). To assess spatial (lower vs. upper intertidal zones) and seasonal (summer vs. winter) variability, we measured soil-air CO2 and CH4 fluxes at low spring tide, analyzing elementary (C, N, and P), isotopic (δ13C and δ15N), and the molecular (n-alkanes and sterols) composition of surface soil OM. A general trend of OM composition was found with increasing urban influence, with higher δ15N (proxy of anthropogenic N enrichment), less negative δ13C, more short-chain n-alkanes, lower C:N ratio (proxies of algal biomass), and higher epicoprostanol content (proxies of sewage-derived OM). The CO2 efflux from exposed soils increased greatly in median (25/75 % interquartile range) from 4.6 (2.9/8.3) to 24.0 (21.5/32.7) mmol m-2 h-1 from more pristine to more urbanized watersheds, independent of intertidal zone and seasonality. The CO2 fluxes at the most eutrophicated site were among the highest reported worldwide for mangrove soils. Conversely, CH4 emissions were relatively low (three orders of magnitude lower than CO2 fluxes), with high peaks in the lower intertidal zone during the rainy summer. Thus, our findings demonstrate the influence of coastal eutrophication on global warming potentials related to enhanced heterotrophic remineralization of blue carbon within mangrove soils.

Tropical forests as drivers of lake carbon burial.

A significant proportion of carbon (C) captured by terrestrial primary production is buried in lacustrine ecosystems, which have been substantially affected by anthropogenic activities globally. However, there is a scarcity of sedimentary organic carbon (OC) accumulation information for lakes surrounded by highly productive rainforests at warm tropical latitudes, or in response to land cover and climate change. Here, we combine new data from intensive campaigns spanning 13 lakes across remote Amazonian regions with a broad literature compilation, to produce the first spatially-weighted global analysis of recent OC burial in lakes (over ~50-100-years) that integrates both biome type and forest cover. We find that humid tropical forest lake sediments are a disproportionately important global OC sink of ~80 Tg C yr-1 with implications for climate change. Further, we demonstrate that temperature and forest conservation are key factors in maintaining massive organic carbon pools in tropical lacustrine sediments.

Dataset on the RETRO-BMC cruise onboard the R/V Hespérides, April 2017, Brazil-Malvinas Confluence.

This dataset, gathered during the RETRO-BMC cruise, reports multiple-scale measurements at the Confluence of the Brazil and Malvinas Currents. The cruise was carried out between 8 and 28 April 2017 onboard R/V Hespérides, departing from Ushuaia and arriving to Santos. Along its track, the vessel recorded near-surface temperature and salinity, as well as the horizontal flow from 20 m down to about 800 m. A total of 33 hydrographic stations were completed in a region off the Patagonian Shelf, within 41.2°S-35.9°S and out to 53.0°W. At each station, a multiparametric probe and velocity sensors were deployed inside the frame of a rosette used to collect water samples at selected depths; these samples were later used for several water analyses, including inorganic nutrient concentrations. Microstructure measurements were carried out in 11 of these hydrographic stations. In addition, two high-resolution three-dimensional surveys were conducted with an instrumented undulating vehicle between 40.6°S-39.0°S and 55.6°W-53.8°W. Lastly, eight high-frequency vertical profilers were deployed in the region and five position-transmitting drifters were launched. These data allow the description of the Confluence from the regional scale to the microscale, and provide a view of the variability of the frontal region on time scales from days to weeks.

Structure, function and resilience to desiccation of methanogenic microbial communities in temporarily inundated soils of the Amazon rainforest (Cunia Reserve, Rondonia).

The floodplain of the Amazon River is a large source for the greenhouse gas methane, but the soil microbial communities and processes involved are little known. We studied the structure and function of the methanogenic microbial communities in soils across different inundation regimes in the Cunia Reserve, encompassing nonflooded forest soil (dry forest), occasionally flooded Igapo soils (dry Igapo), long time flooded Igapo soils (wet Igapo) and sediments from Igarape streams (Igarape). We also investigated a Transect (four sites) from the water shoreline into the dry forest. The potential and resilience of the CH4 production process were studied in the original soil samples upon anaerobic incubation and again after artificial desiccation and rewetting. Bacterial and archaeal 16S rRNA genes and methanogenic mcrA were always present in the soils, except in dry forest soils where mcrA increased only upon anaerobic incubation. NMDS analysis showed a clear effect of desiccation and rewetting treatments on both bacterial and archaeal communities. However, the effects of the different sites were less pronounced, with the exception of Igarape. After anaerobic incubation, methanogenic taxa became more abundant among the Archaea, while there was only little change among the Bacteria. Contribution of hydrogenotrophic methanogenesis was usually around 40%. After desiccation and rewetting, we found that Firmicutes, Methanocellales and Methanosarcinaceae became the dominant taxa, but rates and pathways of CH4 production stayed similar. Such change was also observed in soils from the Transects. The results indicate that microbial community structures of Amazonian soils will in general be strongly affected by flooding and drainage events, while differences between specific field sites will be comparatively minor.

Erratum: Large emissions from floodplain trees close the Amazon methane budget.

This corrects the article DOI: 10.1038/nature24639.

Large emissions from floodplain trees close the Amazon methane budget.

Wetlands are the largest global source of atmospheric methane (CH4), a potent greenhouse gas. However, methane emission inventories from the Amazon floodplain, the largest natural geographic source of CH4 in the tropics, consistently underestimate the atmospheric burden of CH4 determined via remote sensing and inversion modelling, pointing to a major gap in our understanding of the contribution of these ecosystems to CH4 emissions. Here we report CH4 fluxes from the stems of 2,357 individual Amazonian floodplain trees from 13 locations across the central Amazon basin. We find that escape of soil gas through wetland trees is the dominant source of regional CH4 emissions. Methane fluxes from Amazon tree stems were up to 200 times larger than emissions reported for temperate wet forests and tropical peat swamp forests, representing the largest non-ebullitive wetland fluxes observed. Emissions from trees had an average stable carbon isotope value (δ13C) of -66.2 ± 6.4 per mil, consistent with a soil biogenic origin. We estimate that floodplain trees emit 15.1 ± 1.8 to 21.2 ± 2.5 teragrams of CH4 a year, in addition to the 20.5 ± 5.3 teragrams a year emitted regionally from other sources. Furthermore, we provide a 'top-down' regional estimate of CH4 emissions of 42.7 ± 5.6 teragrams of CH4 a year for the Amazon basin, based on regular vertical lower-troposphere CH4 profiles covering the period 2010-2013. We find close agreement between our 'top-down' and combined 'bottom-up' estimates, indicating that large CH4 emissions from trees adapted to permanent or seasonal inundation can account for the emission source that is required to close the Amazon CH4 budget. Our findings demonstrate the importance of tree stem surfaces in mediating approximately half of all wetland CH4 emissions in the Amazon floodplain, a region that represents up to one-third of the global wetland CH4 source when trees are combined with other emission sources.

Structure and function of methanogenic microbial communities in sediments of Amazonian lakes with different water types.

Tropical lake sediments are a significant source for the greenhouse gas methane. We studied function (pathway, rate) and structure (abundance, taxonomic composition) of the microbial communities (Bacteria, Archaea) leading to methane formation together with the main physicochemical characteristics in the sediments of four clear water, six white water and three black water lakes of the Amazon River system. Concentrations of sulfate and ferric iron, pH and δ13 C of organic carbon were usually higher, while concentrations of carbon, nitrogen and rates of CH4 production were generally lower in white water versus clear water or black water sediments. Copy numbers of bacterial and especially archaeal ribosomal RNA genes also tended to be relatively lower in white water sediments. Hydrogenotrophic methanogenesis contributed 58 ± 16% to total CH4 production in all systems. Network analysis identified six communities, of which four were comprised mostly of bacteria found in all sediment types, while two were mostly in clear water sediment. Terminal restriction fragment length polymorphism (T-RFLP) and pyrosequencing showed that the compositions of the communities differed between the different sediment systems, statistically related to the particular physicochemical conditions and to CH4 production rates. Among the archaea, clear water, white water, and black water sediments contained relatively more Methanomicrobiales, Methanosarcinaceae and Methanocellales, respectively, while Methanosaetaceae were common in all systems. Proteobacteria, Deltaproteobacteria (Myxococcales, Syntrophobacterales, sulfate reducers) in particular, Acidobacteria and Firmicutes were the most abundant bacterial phyla in all sediment systems. Among the other important bacterial phyla, clear water sediments contained relatively more Alphaproteobacteria and Planctomycetes, whereas white water sediments contained relatively more Betaproteobacteria, Firmicutes, Actinobacteria, and Chloroflexi than the respective other sediment systems. The data showed communities of bacteria common to all sediment types, but also revealed microbial groups that were significantly different between the sediment types, which also differed in physicochemical conditions. Our study showed that function of the microbial communities may be understood on the basis of their structures, which in turn are determined by environmental heterogeneity.

Spatial versus day-to-day within-lake variability in tropical floodplain lake CH4 emissions--developing optimized approaches to representative flux measurements.

Inland waters (lakes, rivers and reservoirs) are now understood to contribute large amounts of methane (CH4) to the atmosphere. However, fluxes are poorly constrained and there is a need for improved knowledge on spatiotemporal variability and on ways of optimizing sampling efforts to yield representative emission estimates for different types of aquatic ecosystems. Low-latitude floodplain lakes and wetlands are among the most high-emitting environments, and here we provide a detailed investigation of spatial and day-to-day variability in a shallow floodplain lake in the Pantanal in Brazil over a five-day period. CH4 flux was dominated by frequent and ubiquitous ebullition. A strong but predictable spatial variability (decreasing flux with increasing distance to the shore or to littoral vegetation) was found, and this pattern can be addressed by sampling along transects from the shore to the center. Although no distinct day-to-day variability were found, a significant increase in flux was identified from measurement day 1 to measurement day 5, which was likely attributable to a simultaneous increase in temperature. Our study demonstrates that representative emission assessments requires consideration of spatial variability, but also that spatial variability patterns are predictable for lakes of this type and may therefore be addressed through limited sampling efforts if designed properly (e.g., fewer chambers may be used if organized along transects). Such optimized assessments of spatial variability are beneficial by allowing more of the available sampling resources to focus on assessing temporal variability, thereby improving overall flux assessments.

Experimental evidence of nitrogen control on pCO(2) in phosphorus-enriched humic and clear coastal lagoon waters.

Natural and human-induced controls on carbon dioxide (CO(2)) in tropical waters may be very dynamic (over time and among or within ecosystems) considering the potential role of warmer temperatures intensifying metabolic responses and playing a direct role on the balance between photosynthesis and respiration. The high magnitude of biological processes at low latitudes following eutrophication by nitrogen (N) and phosphorus (P) inputs into coastal lagoons waters may be a relevant component of the carbon cycle, showing controls on partial pressure of CO(2) (pCO(2)) that are still poorly understood. Here we assessed the strength of N control on pCO(2) in P-enriched humic and clear coastal lagoons waters, using four experimental treatments in microcosms: control (no additional nutrients) and three levels of N additions coupled to P enrichments. In humic coastal lagoons waters, a persistent CO(2) supersaturation was reported in controls and all nutrient-enriched treatments, ranging from 24- to 4-fold the atmospheric equilibrium value. However, both humic and clear coastal lagoons waters only showed significant decreases in pCO(2) in relation to the controlled microcosms in the two treatments with higher N addition levels. Additionally, clear coastal lagoons water microcosms showed a shift from CO(2) sources to CO(2) sinks, in relation to the atmosphere. Only in the two more N-enriched treatments did pCO(2) substantially decrease, from 650 µatm in controls and less N-enriched treatments to 10 µatm in more N-enriched microcosms. Humic substrates and N inputs can modulate pCO(2) even in P-enriched coastal lagoons waters, thereby being important drivers on CO(2) outgassing from inland waters.

Synergistic control of CO2 emissions by fish and nutrients in a humic tropical lake.

Using experimental mesocosms, we tested the strength of bottom-up controls by nutrients and top-down controls by an omnivorous fish (Hyphessobrycon bifasciatus; family Characidae), and the interaction between them on the CO(2) partial pressure (pCO(2)) in the surface waters of a tropical humic lake (Lake Cabiúnas, Brazil). The experiment included the addition of nutrients and fish to the mesocosms in a factorial design. Overall, persistent CO(2) emissions to the atmosphere, supported by an intense net heterotrophy, were observed in all treatments and replicates over the 6-week study period. The CO(2) efflux (average ± standard error) integrated over the experiment was similar among the control mesocosms and those receiving only fish or only nutrients (309 ± 2, 303 ± 16, and 297 ± 17 mmol CO(2) m(-2) day(-1), respectively). However, the addition of nutrients in the presence of fish resulted in a high algal biomass and daytime net autotrophy, reducing the CO(2) emissions by 35% (by 193 ± 7 mmol CO(2) m(-2) day(-1)). These results indicate that high CO(2) emissions persist following the eutrophication of humic waters, but that the magnitude of these emissions might depend on the structure of the food web. In conclusion, fish and nutrients may act in a synergistic manner to modulate persistent CO(2) emissions from tropical humic lakes.

Methane emissions from Pantanal, South America, during the low water season: toward more comprehensive sampling.

Freshwater environments contribute 75% of the natural global methane (CH(4)) emissions. While there are indications that tropical lakes and reservoirs emit 58-400% more CH(4) per unit area than similar environments in boreal and temperate biomes, direct measurements of tropical lake emissions are scarce. We measured CH(4) emissions from 16 natural shallow lakes in the Pantanal region of South America, one of the world's largest tropical wetland areas, during the low water period using floating flux chambers. Measured fluxes ranged from 3.9 to 74.2 mmol m(-2) d(-1) with the average from all studied lakes being 8.8 mmol m(-2) d(-1) (131.8 mg CH(4) m(-2) d(-1)), of which ebullition accounted for 91% of the flux (28-98% on individual lakes). Diel cycling of emission rates was observed and therefore 24-h long measurements are recommended rather than short-term measurements not accounting for the full diel cycle. Methane emission variability within a lake may be equal to or more important than between lake variability in floodplain areas as this study identified diverse habitats within lakes having widely different flux rates. Future measurements with static floating chambers should be based on many individual chambers distributed in the various subenvironments of a lake that may differ in emissions in order to account for the within lake variability.

A chitin-like component in Aedes aegypti eggshells, eggs and ovaries.

An insoluble white substance was prepared from extracts of eggshells of Aedes aegypti, the yellow fever mosquito and dengue vector. Its infrared and proton NMR spectra were similar to that of standard commercial chitin. This putative chitin-like material, also obtained from ovaries, newly laid and dark eggs, was hydrolyzed in acid and a major product was identified by HPLC to be glucosamine. The eggshell acid hydrolysate was also analyzed by ESI-MS and an ion identical to a glucosamine monoprotonated species was detected. The presence of chitin was also analyzed during different developmental stages of the ovary using a fluorescent microscopy technique and probes specific for chitin. The results showed that a chitin-like material accumulates in oocytes during oogenesis. Streptomyces griseus chitinase pre-treatment of oocytes greatly reduced the chitin-derived fluorescence. Chitinase activity was detected in newborn larvae and eggs prior to hatching. Feeding experiments indicated that the chitin synthesis inhibitor lufenuron inhibited chitin synthesis, either when mosquitoes were allowed to feed directly on lufenuron-treated chickens or when an artificial feeding system was used. Lufenuron inhibited egg hatch, larval development and reduced mosquito viability. These data demonstrate for the first time that (1) a chitin-like material is present in A. aegypti eggs, ovaries and eggshells; (2) a chitin synthesis inhibitor can be used to inhibit mosquito oogenesis; and (3) chitin synthesis inhibitors have potential for controlling mosquito populations.